That is why pressure increases much more than linearly with the powder increase. It typically increases by something like the square or even the cube of the powder charge increase. For example, increase powder charge by 5% and the pressure goes up by something between 10% (because 1.05 squared = 1.05 x 1.05 = 1.1025) and 16% (because 1.05 cubed = 1.05 x1.05 x 1.05 = 1.157625). At least, that is about how it works when the powder is burning within the pressure range it was designed for.

That is the reason for the well-known empirical result of approximately liner bullet muzzle velocity increase with powder increase. Increasing the velocity increases the bullet's energy by the square of the velocity increase. To achieve that, just adding energy in the form of more powder would not be enough. What happens is that ALL of the powder is also burnng faster, so more energy is released from the powder faster, pushing the bullet harder and earlier. That makes the overall efficiency higher for converting the chemical energy in the powder to kinetic energy in the bullet.

So, in summary, adding powder will actually give you LESS unburned powder, because it makes the powder burn faster.

But, N110 is pretty slow for a hanadgun, so you may always have a little unburned powder in a 4" barrel with a magnum cartridge, at least at pressures you want to have occur inside a gun you are holding in your hand.